Collation shrink

ABSTRACT

The invention relates to a film structure combining a metallocene-rich layer and an HDPE-containing layer. A preferred embodiment is a structure having metallocene-rich skin layers and an HDPE-containing core. The structures of the invention are particularly useful for collation shrink.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a Continuation-in-Part of U.S. applicationSer. No. 10/669,221, filed 24 Sep. 2003 now U.S. Pat. No. 7,422,786.

FIELD OF THE INVENTION

The invention relates to co-extruded structures for collation shrinkfilms and blends of polyethylene used therefor.

BACKGROUND OF THE INVENTION

Collation shrink concerns the bundling of items together using heatshrinkable film. Collation shrink is used for a very wide variety ofapplications and notably for the secondary packaging of food or drinks.Examples include metal cans and plastic bottles.

Typically, films are applied at room temperature and placed under a heatsource to shrink. Suitable performance characteristics on the shrinkpackaging line include sufficient stiffness allowing the film to becorrectly wrapped around the items being packaged, sufficientdimensional shrinkage to ensure a snug fit, and a low enough Coefficientof Friction (COF) for machinability and package handling. Filmsappropriate for use as collation shrink must have a high thermal shrinkforce to ensure a tight fit and high tensile strength to withstandhandling and abuse during transportation.

In addition, the packaging must have excellent display propertiesincluding gloss (preferably under different angles to maximize appeal),haze (or “contact clarity”) and clarity (“see-through clarity”).

Finally, the collation shrink film manufacturer wants the properties ofa low melt pressure, and the ability to use low motor power, bothallowing higher production rates.

While it is known how to improve many of the above propertiesindividually, currently available structures do not combine all of theproperties satisfactorily in a film having sufficiently thin gauge to becommercially attractive.

Polyethylene is an attractive component to use in collation shrink film.Various types of polyethylenes are known in the art. Low densitypolyethylene (“LDPE”) can be prepared at high pressure using freeradical initiators and typically has a density in the range of0.916-0.940 g/cm³. LDPE is also known as “branched” or “heterogeneouslybranched” polyethylene because of the relatively large number of longchain branches extending from the main polymer backbone. Polyethylene inthe same density range, i.e., 0.916 to 0.940 g/cm³, which is linear anddoes not contain large quantities of long chain branching is also known;this “linear low density polyethylene” (“LLDPE”) can be produced withconventional Ziegler-Natta catalysts or with single site catalysts—suchas metallocene catalysts. Relatively higher density LDPE or LLDPE,typically in the range of 0.928 to 0.940 g/cm³ are sometimes referred toas medium density polyethylene (“MDPE”) or Linear Medium DensityPolyethylene (LMDPE). Polyethylenes having still greater density are thehigh density polyethylenes (“HDPEs”), i.e., polyethylenes havingdensities greater than 0.940 g/cm³, and are generally prepared withZiegler-Natta catalysts, chrome catalysts or even single site catalystssuch as metallocene catalysts. Very low density polyethylene (“VLDPE”)is also known. VLDPEs can be produced by a number of different processesyielding polymers with different properties, but can be generallydescribed as polyethylenes having a density less than 0.916 g/cm³,typically 0.890 to 0.915 g/cm³ or 0.900 to 0.915 g/cm³.

U.S. Pat. No. 6,187,397 teaches a 3-layer co-extruded heat-shrinkablefilm devoid of metallocene polyethylene. The patent teaches that priorart “high clarity” heat-shrinkable polyethylene films are obtained bycoextrusion of three layers comprising a central layer of predominantly(>50 wt. %) free-radical polyethylene having a relative density of0.918-0.930, optionally with HDPE to confer stiffness, sandwichedbetween two layers of predominantly (80-90 wt. %) metallocene linearpolyethylene having a density of 0.918-0.927.

U.S. Pat. No. 6,340,532 discloses shrink films manufactured from“pseudohomogeneous” linear low density polyethylene resins preferablyprepared with an advanced Ziegler Natta catalyst. Various deficienciesof “homogeneous” resins, i.e., metallocene resins, used in prior artshrink films are discussed.

U.S. Pat. No. 6,368,545 teaches a high clarity multilayer blowncoextruded film prepared using special methods, wherein a film isdescribed having a central core of HDPE.

U.S. Pat. Application No. 20020187360 is directed to a heat shrinkable,co-extruded polyethylene film laminate having a relatively low meltingpoint core layer comprising a linear low density polyethylene (LLDPE)having a density of 0.910-0.930 g/cm³ and a linear very low densitypolyethylene (VLDPE) having a density of 0.880-0.915 g/cm³, sandwichedbetween two relatively higher melting point surface layers comprising alinear low density polyethylene and a linear high density polyethylene.

WO 01/44365 describes a homogeneous blend of a metallocene-catalyzedmedium density polyethylene (mMDPE) with a low density polyethylene(LDPE) to produce blown films. The blend may be coextruded betweenlayers of LDPE to make blown films taught in the reference as having thegood optical properties of LDPE and the good mechanical and processingproperties of MDPE.

Additional patents of interest include U.S. Pat. No. 6,492,010, U.S.Statutory Invention Registration H2073, WO 95/00333 and EP 0597502.

The high gloss provided by metallocene polyethylenes is a veryattractive property. However, film layers comprising metallocenepolyethylene have a very high coefficient of friction in the absence ofspecific additives. These additives, in turn, detract from the opticalproperties desired in collation shrink films. A film exploiting the highgloss capabilities of metallocene polyethylene that can be producedefficiently and having the properties sought in a collation shrink filmis highly desirable.

The present inventor has surprisingly discovered that an improvedcollation shrink film may be achieved by a structure having a core layercomprising HDPE and skin layers comprising metallocene polyethylene andoptionally at least one of HDPE or LDPE resins.

SUMMARY OF THE INVENTION

The invention is directed to a film structure having at least twolayers: a layer comprising HDPE and layer comprising ametallocene-catalyzed polyethylene (hereinafter mPE), optionally furthercomprising at least one of HDPE or LDPE. The invention is furtherdirected to a collation shrink-wrapped structure comprising theaforementioned film shrink wrapped around various items.

In a preferred embodiment the film structure comprises a core layercomprising HDPE sandwiched by two metallocene skin layers. In a morepreferred embodiment at least one of said metallocene skin layersfurther comprises at least one of HDPE or LDPE.

It is an object of the present invention to provide various embodimentsof the aforementioned inventions having unique properties, particularlywith respect to optical, strength, and processing properties, as well asperformance in the resultant shrink-wrapped structure.

Another object of the present invention is to provide a collation shrinkfilm having suitable performance on the shrink packaging line.

Still another object of the present invention to provide a shrinkcollation film having appropriate properties to handle abuse duringtransportation.

Yet another object of the present invention to provide shrink wrappedstructure having attractive display properties at the point of sale.

These and other objects, features, and advantages will become apparentas reference is made to the following detailed description, preferredembodiments, examples, and appended claims.

DETAILED DESCRIPTION

In an embodiment, a film structure is provided having at least twolayers. One layer, referred to herein as the first layer and in anembodiment as the core layer, comprises a high density polyethylene(hereinafter “HDPE”) and the second layer, also referred to herein as atleast one skin layer, comprises a single-site catalyzed polyethylenesuch as metallocene polyethylene or mPE.

As used herein, HDPE means polyethylene having a density of greater than0.940 g/cm³. The terms “high density polyethylene” polymer and “HDPE”polymer refer to a homopolymer or copolymer of ethylene having a densitygreater than 0.940 g/cm. Polymers having more than two types ofmonomers, such as terpolymers, are also included within the term“copolymer” as used herein.

The comonomers that are useful in general for making HDPE copolymersuseful in the present invention include alpha-olefins, such as C₃-C₂₀alpha-olefin and preferably C₃-C₁₂ alpha-olefins. The alpha-olefincomonomer can be linear or branched, and two or more comonomers can beused, if desired. Examples of suitable comonomers include linear C₃-C₁₂alpha-olefins, and alpha-olefins having one or more C₁-C₃ alkylbranches, or an aryl group. Specific examples include propylene;3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-butene; 1-pentenewith one or more methyl, ethyl or propyl substituents; 1-hexene;1-hexene with one or more methyl, ethyl or propyl substituents;1-heptene with one or more methyl, ethyl or propyl substituents;1-decene; 1-dodecene; 1-octene with one or more methyl, ethyl or propylsubstituents; 1-nonene with one or more methyl, ethyl or propylsubstituents; ethyl, methyl or dimethyl-substituted 1-decene;1-dodecene; and styrene. It should be appreciated that the list ofcomonomers above is merely exemplary, and is not intended to belimiting.

Preferred comonomers include propylene, 1-butene, 1-pentene,4-methyl-1-pentene, 1-hexene, 1-octene and styrene. Other usefulcomonomers include polar vinyl, conjugated and non-conjugated dienes,acetylene and aldehyde monomers, which can be included in minor amountsin terpolymer compositions. Non-conjugated dienes useful as co-monomerspreferably are straight chain, hydrocarbon di-olefins orcycloalkenyl-substituted alkenes, having 6 to 15 carbon atoms. Suitablenon-conjugated dienes include, for example: (a) straight chain acyclicdienes, such as 1,4-hexadiene and 1,6-octadiene; (b) branched chainacyclic dienes, such as 5-methyl-1,4-hexadiene;3,7-dimethyl-1,6-octadiene; and 3,7-dimethyl-1,7-octadiene; (c) singlering alicyclic dienes, such as 1,4-cyclohexadiene; 1,5-cyclo-octadieneand 1,7-cyclododecadiene; (d) multi-ring alicyclic fused and bridgedring dienes, such as tetrahydroindene; norbornadiene;methyl-tetrahydroindene; dicyclopentadiene (DCPD);bicyclo-(2.2.1)-hepta2,5-diene; alkenyl, alkylidene, cycloalkenyl andcycloalkyl idene norbornenes, such as 5-methylene-2-norbornene (NINB),5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene,5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene, and5-vinyl-2-norbornene (VNB); and (e) cycloalkenyl-substituted alkenes,such as vinyl cyclohexene, allyl cyclohexene, vinyl cyclooctene, 4-vinylcyclohexene, allyl cyclodecene, and vinyl cyclododecene. Of thenon-conjugated dienes typically used, the preferred dienes aredicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbornene, and5-ethylidene-2-norbornene. Particularly preferred diolefins, are5-ethylidene-2-norbornene (ENB), 1,4-hexadiene, dicyclopentadiene(DCPD), norbornadiene, and 5-vinyl-2norbornene (VNB).

The amount of comonomer used will depend upon the desired density of theHDPE polymer and the specific comonomers selected, taking into accountprocessing conditions such as temperature and pressure and other factorssuch as the presence or absence of telomers and the like, as would beapparent to one of ordinary skill in the art in possession of thepresent disclosure.

In one embodiment, the HDPE polymer has a density of greater than 0.940g/cm³, preferably from about 0.940 g/cm to about 0.970 g/cm³, morepreferably from about 0.955 g/cm³ to about 0.965 g/cm³, and mostpreferably from about 0.960 g/cm³ to about 0.965 g/cm³. Densitiesreferred to herein are in accordance with ASTM D 1505.

In one embodiment, the HDPE polymer may have a melt index from 0.01 to45 g/10 min, as measured in accordance with ASTM-1238 condition E. TheHDPE polymer may be produced using any conventional polymerizationprocess, such as a solution, a slurry, or a gas-phase process, and asuitable catalyst, such as a chrome catalyst, a Ziegler-Natta catalystor a metallocene catalyst. It is preferred that the HDPEs used in theblends according to the present invention be produced usingZiegler-Natta catalysts.

Examples of suitable HDPE useful in the present invention include HDPEsavailable from ExxonMobil Chemical Co., Houston, Tex., under the HD,HDA, HMA, HRA, HRP, HDZ or HYA series or under the trademark PAXON.Examples of HDPE include HYA800, produced in the gas phase, and HDZ222,produced by the stirred slurry process. Blends of two or more HDPEpolymers and one or more HDPE polymers with one or more non-HDPEpolymers are also contemplated.

The HDPE component of the first layer (or, in the case of an embodimentcomprising three layers, the HDPE component of the “core layer”,described more fully below) should be present in the amount of betweenabout 1 wt. % and 50 wt. %, preferably between about 10 wt. % and 50 wt.%, more preferably between about 15 wt. % and 45 wt. %.

This first layer (or, in an embodiment, core layer) should also comprisefrom between about 99 wt. % and 50 wt. % LDPE, preferably between about90 wt. % and 50 wt. %, more preferably between about 85 wt. % and 55 wt.%, even more preferably between about 85 wt. % and about 65 wt. % LDPE.In a preferred embodiment the first layer can also comprise anotherpolyolefin, such as LLDPE (e.g., a tri-blend).

The LDPE suitable for use in the present invention is free-radicalinitiated LDPE having a density in the range of 0.916 to 0.940 g/cm³,preferably 0.924 to 0.940 g/cm³. In an embodiment, the LDPE blended withthe HDPE in this first layer or core layer has a density in the range of0.916 to 0.935 g/cm³, more preferably 0.926 to 0.935 g/cm³. In anotherembodiment, the LDPE blended with the HDPE in this layer has a densityin the range of 0.916 to 0.927 g/cm³, and more preferably 0.921 to 0.926g/cm³. Other embodiments include LDPEs having densities from any of thelower density limits specified to any of the higher density limitsspecified herein, for example, 0.921 to 0.940 g/cm³ and 0.926 to 0.940g/cm³. Preferred specific LDPEs are LD170BA and experimental gradesEX489BA and EX514BA, also available from ExxonMobil Chemical Co.,Houston, Tex.

Additional polyolefins may be added, such as VLDPE, provided that thatthe aforementioned wt. % of HDPE and LDPE is met. Likewise, the blend ofHDPE and LDPE may include various additives, as discussed in more detailbelow. However, in an embodiment it is preferred that the blend of HDPEand LDPE comprising the first layer or core layer of the film structuredoes not contain slip or antiblock additives. In a preferred embodiment,this layer contains no metallocene polyethylene. In another embodiment,mPE may be added, particularly in the case where additional toughness isrequired. The composition of this layer may further comprisepolypropylene or it may be without polypropylene. Other nonlimitingexamples of embodiments of the invention include combinations of theabove recited embodiments, such as the HDPE/LDPE blend of the inventionwithout slip or antiblock additives, without a metallocene polyethylene,and without polypropylene, an embodiment comprising HDPE/LDPE blend ofthe invention without slip or antiblock additive, and with a metallocenepolyethylene, and the like.

The second layer of the film structure according to the presentinvention, which in an embodiment is a skin layer around the core layerdescribed above, comprises a single-site catalyzed polyethylene such asmetallocene polyethylene (mPE). In a preferred embodiment, the mPE is alinear low density polyethylene (hereinafter “mLLDPE”). In anotherpreferred embodiment the mPE is a VLDPE (hereinafter “mVLDPE”) having adensity of between about 0.880 to 0.915 g/cm³. In the case where theHDPE component of the blend is also a metallocene polyethylene, thesecond component of the invention must be a mLLDPE or the aforementionedmVLDPE.

A “metallocene polyethylene” as used herein means a polyethyleneproduced by a metallocene catalyst. As used herein, the term“metallocene catalyst” is defined to be at least one metallocenecatalyst component containing one or more substituted or unsubstitutedcyclopentadienyl moiety (Cp) in combination with a Group 4, 5, or 6transition metal (M).

The metallocene catalyst precursors generally require activation with asuitable co-catalyst, or activator, in order to yield an “activemetallocene catalyst”, i.e., an organometallic complex with a vacantcoordination site that can coordinate, insert, and polymerize olefins.The active catalyst systems generally includes not only the metallocenecomplex, but also an activator, such as an alumoxane or a derivativethereof (preferably MAO), an ionizing activator, a Lewis acid, or acombination thereof. Alkylalumoxanes are additionally suitable ascatalyst activators. The catalyst system is preferably supported on acarrier, typically an inorganic oxide or chloride or a resinous materialsuch as polyethylene.

The prior art is replete with examples of metallocene catalysts/systemsfor producing polyethylene. Non-limiting examples of metallocenecatalysts and catalyst systems useful in practicing the presentinvention include WO 96/11961; WO 96/11960; U.S. Pat. Nos. 4,808,561;5,017,714; 5,055,438; 5,064,802; 5,124,418; 5,153,157; 5,324,800; morerecent examples are U.S. Pat. Nos. 6,380,122; and 6,376,410; andWO01/98409, and references cited therein. Included within the definitionof mPE resins, and more particularly mLLDPE resins, for the purpose ofthe present invention, are polyethylene resins having a lowpolydispersity as described, for instance, in the aforementioned U.S.Pat. No. 6,492,010, that is, a polydispersity produced by a catalystvariously described as single site, constrained geometry, or metallocenecatalyst, catalysts per se well known in the prior art. Preferred lowpolydispersity mPEs are mLLDPEs having a density within the range forLLDPEs as set forth herein. The low polydispersity mLLDPE resins may beprepared from a partially crystalline polyethylene resin that is apolymer prepared with ethylene, preferably ethylene and at least onealpha olefin monomer, e.g., a copolymer or terpolymer. The alpha olefinmonomer generally has from about 3 to about 12 carbon atoms, preferablyfrom about 4 to about 10 carbon atoms, and more preferably from about 6to about 8 carbon atoms. The alpha olefin comonomer content is generallybelow about 30 weight percent, preferably below about 20 weight percent,and more preferably from about 1 to about 15 weight percent. Exemplarycomonomers include propylene, 1-butene, 1-pentene, 1-hexene,3-methyl-1-pentene, 4-methyl-1-pentene, 1-octene, 1-decene, and1-dodecene.

In an embodiment, low polydispersity resins will have average molecularweights in the range of from about 20,000 to about 500,000, preferablyfrom about 50,000 to about 200,000. The molecular weight is determinedby commonly used techniques such as size exclusion chromatography or gelpermeation chromatography.

In an embodiment, the low polydispersity polymer will have a molecularweight distribution, or polydispersity, (Mw/Mn, “MWD”) within the rangeof about 1 to about 4, preferably about 1.5 to about 4, more preferablyabout 2 to about 4, and even more preferably from about 2 to about 3.Such products are well known in the art per se and are discussed in U.S.Pat. Nos. 5,907,942; 5,907,943; 5,902,684; 5,752,362; 5,814,399; and5,749,202.

In an embodiment, the low polydispersity polymers thus producedgenerally have a crystalline content in excess of at least 10 weightpercent, generally in excess of at least 15 weight percent.

Preferred mLLDPE resins will be characterized by one or more of theaforementioned embodiments, including preferred, more preferred, etc. Asa non-limiting limiting example, a preferred mLLDPE according to thepresent invention is characterized as having a molecular weight of from20,000 to 500,000 and a polydispersity of from about 2 to about 4;another preferred mLLDPE according to the present invention ischaracterized as having a polydispersity of from about 1 to about 4 anda crystalline content in excess of at least 10 wt. %.

Useful low polydispersity or mLLDPE polymers are available from, amongothers, Dow Chemical Company and Exxon Chemical Company who areproducers of single site or constrained geometry catalyzedpolyethylenes. These resins are commercially available as the ENHANCEDPOLYETHYLENE™, ELITE™, AFFINITY™, EXXACT™, and EXCEED™ polyethyleneresins.

Also included within the definition of mLLDPE according to the presentinvention are bimodal resins produced by catalysts having as at leastone component a single site or constrained geometry catalyst whichproduces a low polydispersity polymer. Particularly preferred examplesare bimodal resins having as a component a resin produced using a singlesite, constrained geometry, or metallocene catalyst and having a densityfalling within the density range for LLDPE as previously described.Bimodal resins are per se well known in the art.

In a more preferred embodiment, useful mPE suitable for the presentinvention include metallocene LLDPE (mLLDPE) under the Exceed™trademark, available from ExxonMobil Chemical Company, Houston, Tex.Particularly preferred is Exceed™ 1327CA polyethylene and Exceed™ 1018CApolyethylene, both commercially available mLLDPEs with a C₆ comonomerincorporated and produced in the gas phase.

In an embodiment, a blend suitable for the second layer or skin layer(s)of the film structure should comprise from between about 100 wt. % and50 wt. % of mPE. Preferably the mPE has a density range of from 0.910 to0.940 g/cm³ and more preferably 0.915 to 0.940 g/cm³, still morepreferably 0.921 to 0.934 g/cm³, yet still more preferably 0.925 to0.929 g/cm³.

Optional components, in the amount of no more than 50 wt. %, includeLDPE and/or HDPE. Preferred LDPEs and HDPE as far as density ranges arethose set forth elsewhere in the present application. Preferredembodiments are also preferably selected from the commercially availableor known LDPEs or HDPEs discussed herein. In another preferredembodiment, LDPEs suitable for use in this second layer are free-radicalinitiated LDPEs having a density in the range of 0.916 to 0.940 g/cm³,preferably 0.924 to 0.940 g/cm³. In an embodiment, the LDPE blended withthe HDPE in this layer has a density in the range of 0.916 to 0.940g/cm³, more preferably 0.921 to 0.935 g/cm³. In another embodiment, theLDPE blended with the HDPE in this layer has a density in the range of0.916 to 0.927 g/cm³, and more preferably 0.921 to 0.926 g/cm³. Again,preferred specific examples of LDPEs are LD170BA and experimental gradesEX489BA and EX514BA, mentioned above. Blends of two or more LDPEs arecontemplated. The LDPE used in this second layer, if at all, may be thesame or different as the LDPE used in the first layer.

Particularly preferred HDPE in this second layer include HDPEs availablefrom ExxonMobil Chemical Co., Houston, Tex., under the HD, HDA, HMA,HRA, HRP, HDZ or HYA series or under the trademark PAXON, particularlyHYA800 and HDZ222, discussed above. Blends of two or more HDPE polymersin this layer are also contemplated.

In the case where HDPE is present in the second layer or skin layer, itmay be the same or different than the HDPE in the first layer. Thus, theHDPE polymer has a density of greater than 0.940 g/cm³. In a preferredembodiment the HDPE in this layer has a density of from about 0.940 g/cmto about 0.970 g/cm³, more preferably from about 0.955 g/cm³ to about0.965 g/cm³, and most preferably from about 0.960 g/cm³ to about 0.965g/cm³. This second layer may include various additives, as discussed inmore detail below. However, it is preferred that this second layer,comprising mPE and optionally HDPE and/or LDPE, does not contain slip orantiblock additives.

Additionally, in embodiments this second or skin layer may include orexclude one or more of the following: additional polyolefins such asVLDPE or polypropylene, slip or antiblock agents, and the like.

Multilayer film forming techniques are well-known to one of ordinaryskill in the art and the prior art is replete with examples; see, forinstance, WO01/98409. Any of these techniques may be used to formmultilayer films according to the present invention, but coextrusion ismost preferred and provides the greatest advantage of the invention asregards collation shrink film structures. Cast films are alsoenvisioned, particularly in the case wherein at least one skin layer, asdescribed more fully below, comprises polypropylene.

While those of skill in the art will appreciate that the thickness oflayers may be adjusted based on the desired end use, one of thesurprising aspects of the present invention is that the composition ofthe layers of the present invention provide for multilayer films havingthe appropriate properties for collation shrink while being ofsufficiently thin gauge to be commercially attractive.

Thus, according to one embodiment of the invention, the first layercomprising HDPE, as described above, and the second layer comprisingmPE, is coextruded to form a multilayer film useful as collation shrinkfilm. In the preferred collation shrink wrapped structure the secondlayer comprising the metallocene polyethylene is the outside layer withthe first layer comprising HDPE in contact with the itemsshrink-wrapped.

In an embodiment the film according to the invention consistsessentially of the first layer comprising HDPE and the second layercomprising mPE. In a more preferred embodiment, the first layer is about30 microns thick and the second layer is about 5 microns thick.

In another embodiment, the first layer comprising HDPE, described above,is a core layer between two skin layers, at least one of which is thesecond layer, comprising mPE, described above. The two skin layers maybe the same or different, provided that at least one is a second layer,as described above, comprising mPE. In this embodiment, it is preferredthat both skin layers also comprise mPE.

As used herein, the term “skin layer” means that the layer is the outerlayer of the structure. Thus, in a three-layer structure there are twoskin layers and a core layer, sandwiched by the skin layers. Thisstructure will be denoted A/B/A, wherein the A layer denotes a skinlayer, corresponding to the second layer comprising mPE, above, and theB layer denotes the core layer, corresponding to the first layerdescribed above. It will be recognized that the A layers do not need tobe identical, however.

In still another embodiment, the structure includes a layer comprisingHDPE without a metallocene polyethylene component, and a layercomprising a blend comprising metallocene polyethylene and HDPE.Optionally, the layer comprising HDPE without a metallocene polyethylenecomponent is sandwiched between two skin layers comprising mLLDPEwherein at least one of the skin layers further comprises HDPE. The skinlayers in any of these “skin and core” (or A/B/A) embodiments may be thesame or different.

Additional film layers are contemplated, e.g., between one or both ofA/B, e.g. as tie-layers. However, in the preferred embodiment the corelayer B comprises HDPE and the skin layers A comprise mPE (i.e.,corresponding to one of the first layers and two of the second layers,respectively, described above). The final film comprising the A/B/Astructure may be symmetrical or it may be unsymmetrical.

In a more preferred embodiment the film according to the presentinvention comprises the A/B/A structure, wherein the A skin layers,which may be the same or different, each independently comprise an mPEhaving a density of between about 0.910 to 0.940 g/cm³, preferably 0.915to 0.940 g/cm³, and optionally an HDPE, preferably having a density ofbetween about 0.940 and 0.970 g/cm³, more preferably 0.955 to about0.965 g/cm³, and most preferably from about 0.960 to about 0.965 g/cm³,and the B core layer comprises an HDPE, preferably having a density ofbetween about 0.940 and 0.970 g/cm³, more preferably 0.955 to about0.965 g/cm³, and most preferably from about 0.960 to about 0.965 g/cm³,and an LDPE, preferably having a density in the range of 0.916 to 0.935g/cm³, more preferably 0.921 to 0.930 g/cm³. In the case where there isHDPE in one or both of the skin layers, the HDPE in each layer isindependently selected and it may be the same or different from theother layer and/or the core layer.

In this preferred A/B/A structure, it is more preferred that the corelayer B comprise 60-90 wt. %, more preferably 70-80 wt. % LDPE, and40-10 wt. % HDPE, more preferably 30-20 wt. %, and that the skin layersA are each independently selected from 80-100 wt. %, preferably 85-95wt. % mPE, and 20-0 wt. % HDPE, more preferably 15-5 wt. %. In apreferred embodiment the A/B/A structure is symmetrical with respect tocomposition and thickness. In another preferred embodiment the A/B/Astructure is no thicker than 50 microns and more preferably about 40microns thick or less.

In another preferred embodiment, in a structure comprising A/B/A layersaccording to the present invention, the A skin layers each independentlycomprise at least one mLLDPE resin and at least one LDPE resin, and theB core layer comprises at least one LDPE resin and at least one HDPEresin. One or more additional layers may be present between the skinlayers and the core, and the structure may be unsymmetrical orsymmetrical so that, for instance, an embodiment includes a structureconsisting of an A layer, tie layer, B layer, tie layer, A layer, astructure consisting of an A layer, tie layer, B layer, A layer, and thelike. A preferred embodiment is the case where the structure consistsessentially of an A layer, a B layer, A layer having a total thicknessof 2 mils (50 microns±10 microns), the layers being in the ratio,respectively, of about 15:70:15. In another preferred embodiment, the Alayers comprise from about 99 to about 80 wt. %, preferably from about98 to about 90 wt. % mLLDPE and from about 1 to about 20 wt. %,preferably from about 2 to about 10 wt. % LDPE. In another preferredembodiment, the B layer comprises from about 90 to about 50 wt. %,preferably from about 85 to about 55 wt. %, more preferably from about85 to about 75 wt. % LDPE, and from about 10 to about 50 wt. %,preferably from about 15 to about 45 wt. %, more preferably 15 to about25 wt. % HDPE. Additional preferred embodiments include combinations ofthe aforementioned embodiments, preferred embodiments and more preferredembodiment, as well as the preferred and more preferred densities foreach of the prospective polyethylenes in this layer as described in theappropriate sections herein. Each of the aforementioned layers may,independently, include or exclude additional ingredients such as slip orantiblock agents and/or additional polyolefins such as polypropyleneand/or VLDPEs. A particularly advantageous embodiment as an A/B/Astructure as described in this paragraph wherein one of the A layersdoes not contain polypropylene and one of the A layers does containpolypropylene. In a preferred collation shrink wrapped structure, thelayer having the polypropylene would be in contact with the at least oneitem collation shrink wrapped.

In yet another embodiment, which may be a modification of any of theprevious embodiments, the second layer or at least one of the skinlayers comprises an mLLDPE, an HDPE, and an LDPE.

In still another embodiment, the structure comprises a skin layercomprising an mPE according to the present invention, a core layercomprising HDPE according to the present invention, and a second skinlayer comprising polypropylene.

In a preferred embodiment, one or more of the layers of the multilayerfilm structure according to the invention may have certain additives,such as thermal stabilizers, but in this preferred embodiment each ofthe compositions of the various layers should specifically exclude slipor antiblock additives. Suitable additives include: fillers such assilica, talc, and the like; antioxidants (e.g., hindered phenolics suchas IRGANOX™ 1010 or IRGANOX™ 1076 available from Ciba-Geigy); phosphites(e.g., IRGAFOS™ 168 available from Ciba-Geigy); anti-cling additives andanti-static additives; tackifiers, such as polybutenes, terpene resins,aliphatic and aromatic hydrocarbon resins, alkali metal and glycerol,stearates and hydrogenated rosins; UV stabilizers; heat stabilizers;release agents; anti-static agents; pigments; colorants; dyes; waxes;and the like.

Any blending required to make the compositions for the layers accordingto the present invention can be formed using conventional equipment andmethods, such as by dry blending the individual components andsubsequently melt mixing in a mixer, or by mixing the componentstogether directly in a mixer, such as a Banbury mixer, a Haake mixer, aBrabender internal mixer, or a single or twin-screw extruder including acompounding extruder and a side-arm extruder used directly downstream ofa polymerization process or prior to film extrusion.

EXAMPLES

In the following examples, three-layer, A/B/A, films according to theinvention and comparative films were produced on a commerciallyavailable extruder from Winmoller & Holscher. The co-extruded structureswere symmetrical, having an inner core of 30 microns thick and two skinslayers each 5 microns thick. Machine conditions were as follows: (a) diediameter: 250 mm; (b) die gap: 1.4 mm; (c) blow-up ratio: 3.0; (d) coreextruder adapter temperature: 200° C.; (e) skin extruder adaptertemperature setting: 190° C.; (f) die temperature: 200° C.

The various products used in the examples of Table 2 are identifiedbelow in Table 1:

TABLE 1 Product Density MI³ Comments ¹HYA800 0.961 0.7 HDPE Gas Phase¹HDZ222 0.964 2.4 Bimodal HDPE ¹LL1201XV 0.9255 0.7 Ziegler-Natta LLDPEC₄ Gas Phase ¹Exceed 0.927 1.3 Metallocene LLDPEC₆ 1327CA Gas Phase¹Exceed 0.918 1.0 Metallocene LLDPE C₆ 1018CA Gas Phase ²EX489BA 0.92850.55 LDPE High Pressure ²EX514BA 0.9285 0.35 LDPE High Pressure¹Commercially available from ExxonMobil ²Development versions. Improvedversus commercially available as LD170BA. ³ASTM D-1238, condition E(2.16 kg load, 190 C)

Films having a thickness of 40 microns were formed using thecompositions given in Table 2. Examples 2-3, 5-6, 8-9 are examples ofthe present invention having skin layers comprising mPE and HDPE, andcore layers comprising HDPE. Examples 11-12, 14-15, and 17-20 areexamples of the present invention having skin layers comprising mPE butno HDPE, with the core layers comprising HDPE. The other examples arefor comparative purposes. The results of various tests performed areshown in Table 3.

Haze is total haze measured according to ASTM D1003; Gloss 60° angle andGloss 20° angle are both measured in accordance with ASTM D2457; Clarityis measured in accordance with ASTM D1746; the Elmendorf Tear values areboth measured in accordance with ASTM D1922; Thermal Force values areboth measured in accordance with ASTM D2838-95, set temperature: 190°C.; relative 1% secant modulus and 10% offset yield are both measured inaccordance with ASTM D882. Thermal force is measured based on ASTMD2838-95 procedure A using a Retramat tester supplied by Prodemat S.A.

TABLE 2 Core Core extruder extruder Composition Skin Layers CompositionMiddle Layer Melt pressure motor power Str. Thickness Ratio ProductRatio Product Ratio Product Ratio Product (Mpa) (% of max) 1 40 μm 95%1327CA 5% HYA800 80% EX489BA 20% LL1201XV 327 32% 2 40 μm 95% 1327CA 5%HYA800 80% EX489BA 20% HYA800 291 31% 3 40 μm 95% 1327CA 5% HDZ222 80%EX489BA 20% HDZ222 273 33% 4 40 μm 95% 1327CA 5% HYA800 70% EX489BA 30%LL1201XV 350 33% 5 40 μm 95% 1327CA 5% HYA800 70% EX489BA 30% HYA800 29230% 6 40 μm 95% 1327CA 5% HDZ222 70% EX489BA 30% HDZ222 271 29% 7 40 μm95% 1327CA 5% HYA800 60% EX489BA 40% LL1201XV 367 35% 8 40 μm 95% 1327CA5% HYA800 60% EX489BA 40% HYA800 306 31% 9 40 μm 95% 1327CA 5% HDZ22260% EX489BA 40% HDZ222 271 29% 10 40 μm 85% 1327CA 15% EX489BA 80%EX489BA 20% LL1201XV 332 32% 11 40 μm 85% 1327CA 15% EX489BA 80% EX489BA20% HYA800 291 30% 12 40 μm 85% 1327CA 15% EX489BA 80% EX489BA 20%HDZ222 276 29% 13 40 μm 85% 1327CA 15% EX489BA 70% EX489BA 30% LL1201XV353 34% 14 40 μm 85% 1327CA 15% EX489BA 70% EX489BA 30% HYA800 298 30%15 40 μm 85% 1327CA 15% EX489BA 70% EX489BA 30% HDZ222 275 30% 16 40 μm85% 1327CA 15% EX489BA 60% EX489BA 40% LL1201XV 367 35% 17 40 μm 85%1327CA 15% EX489BA 60% EX489BA 40% HYA800 304 32% 18 40 μm 85% 1327CA15% EX489BA 60% EX489BA 40% HDZ222 272 30% 19 40 μm 85% 1327CA 15%EX514BA 70% EX514BA 30% HDZ222 294 32% 20 40 μm 85% 1018CA 15% EX489BA70% EX489BA 30% HDZ222 281 30% 22 40 μm 85% LL1201XV 15% EX489BA 70%EX489BA 30% LL1201XV 341 32%

TABLE 3 Run 1 2 3 4 5 6 7 8 9 10 11 Haze 9.6 5.6 5 9.6 6.2 6 10.9 7.56.8 4 4.4 Gloss 60°% 10 13 13.6 9.5 12.9 13.5 9.8 12.3 13.2 13.4 13.5Gloss 20°% 5.4 11.5 13.5 5.9 10.5 12.8 6.5 10.4 12.5 12.6 11.4 1% sec.mod. MD MPa 339 449 429 340 493 492 338 547 564 334 380 1% sec. mod TDMPa 367 512 516 362 544 555 376 633 672 391 459 Clarity % 80 77 93 76 7481 80 74 87 89 82 Elmendorf MD gr/μm 5.9 14.2 9.3 4.3 10.2 9.1 2.3 4.70.9 5.5 7.1 Elmendorf TD gr/μm 6 7.3 7.9 8.3 9.1 9.9 10 12 12.5 6.6 1.4Thermal force MD N/15 mm .07 1.26 1.31 1.04 1.4 1.55 0.98 1.74 1.76 1.011.3 10% offset yield MD MPa 14.8 17.4 16.8 15.0 18.2 18.2 15.0 19.1 19.114.7 16.2 10% offset yield TD MPa 14.4 17.4 16.9 14.6 17.7 18.7 14.618.9 20.0 14.6 16.1 Run 12 13 14 15 16 17 18 19 20 22 Haze 4.4 4.5 4.95.1 4.8 5.9 5.8 5.20. 4.90. 5.20. Gloss 60°% 13.6 13.3 13.5 13.5 13.112.9 13.4 12.560. 13.540. 12.250. Gloss 20°% 13.2 12.6 12.7 13 11.7 10.312.8 10.70. 13.30. 10.30. 1% sec. mod. MD MPa 409 329 444 471 327 488539 426.0. 451.0. 322.0. 1% sec. mod TD MPa 505 382 505 571 385 583 674543.0. 517.0. 371.0. Clarity % 81 74 78 92 85 67 89 83.0 85.0. 83.0.Elmendorf MD gr/μm 13.4 4.6 11 10.6 9.8 3.6 2.3 15.440. 3.960. 5.560.Elmendorf TD gr/μm 8 7.7 10 9.5 5.6 11.9 11.9 7.910. 12.790. 7.520.Thermal force MF N/15 mm 1.42 0.99 1.49 1.54 1 1.57 1.69 1.673. 1.498.1.0. 10% offset yield MD MPa 16.2 14.4 17.0 17.2 14.3 18.0 18.4 16.716.5 14.1 10% offset yield TD MPa 16.7 14.7 16.9 17.8 14.5 18.6 18.917.3 16.4 14.2

Several advantages can be seen in the present invention, according tothe examples. For instance, melt pressure of the core extruder drop whenthe HDPE grades are used in the core as compared to the LLDPE grades(examples 2-3, 5-6, 8-9, 11-12, 14-15, 17-20 versus 1, 4, 7, 10, 13, 16,22).

In the case of the skins comprising metallocene polyethylene and LDPEand the core comprising HDPE (examples 11-12, 14-15, 17-21), the 1%secant Modulus MD and TD values are significantly higher than the casewhere there is no HDPE in the core layer (examples 10, 13, 16, 22).Among other things, 1% secant Modulus provides a measure of thedown-gauging possible using these films. The higher the 1% secantModulus, the lower the gauge (thickness of the film) required to providethe same benefit. Increase in yield strength as measured by 10% offsetyield is also a benefit which opens down-gauging possibilities. Athinner material having the same stiffness and strength (and thus lowercost) is highly sought after.

Likewise, skins comprised of blends of metallocene polyethylene and HDPEsandwiching a core comprising HDPE (examples 2-3, 5-6, and 8-9) hadsuperior 1% secant Modulus relative to examples having cores notcontaining HDPE (examples 1, 4, and 7).

Furthermore, as is apparent from an inspection of the opticalproperties, the increase in strength and/or downgauging whichaccompanies the presence of HDPE in the core and/or skin is notsignificantly offset by loss of clarity or gloss values. Indeed it isparticularly remarkable that Gloss at 20° and 60° are quite similar forexamples according to the present invention, particularly with respectto the examples having HDPE both in the core and skins relative to theexamples having HDPE in the skin but not the core. A small difference inGloss 20° and 60° is important for display purposes, i.e., the angle ofobservance is not important. In Table 3, for instance, it can be seenthat the difference in Gloss 20° and 60° values is about 0.1%, which isnegligible. Typically for examples of the present invention differencesof 2% are observed.

Moreover, examples according to the invention uniformly exhibit superiorElmendorf tear values (higher number being a measure of higherresistance to tearing) and higher thermal force (a measure of holdingforce when shrink wrapped about collated items).

Example 23

A film having an A/B/A structure of 2 mil thickness with a thicknessratio, respectively, of 15:70:15, was produced on a commercial Maachi™coextrusion line. The A layers consisted of about 95 wt. % Exceed 1327CAand about 5 wt. % LD514. The B layer consisted of about 80 wt. % LD514BAand about 20 wt. % HDZ222.

Example 24

A film identical to the above, except that HDZ222 was substituted forthe LD514, was produced in the same manner.

A comparison of Examples 23 and 24 illustrates that a combination of anmLLDPE and LDPE as the skin layer in this particular case results in areduction in COF of about 15%, a modest increase in gloss, and areduction in haze from 10.4 in Example 24 to 5.9 in Example 23.

The invention has been described above with reference to numerousembodiments and specific examples. Many variations will suggestthemselves to those skilled in this art in light of the above detaileddescription. All such obvious variations are within the full intendedscope of the appended claims.

A preferred embodiment is a multilayer film structure having at leastone first layer comprising HDPE and at least one second layer, differentfrom said first layer, comprising a metallocene polyethylene; also morepreferred embodiments, which may be combined where suitable, as would berecognized by one of skill in the art in possession of the presentdisclosure without undue experimentation: wherein said metallocenepolyethylene is an mLLDPE; wherein said first layer further comprisesLDPE in the amount of at least 50 wt. %, based on the composition of thefirst layer; wherein said second layer further comprises at least oneadditional polyolefin selected from group consisting of HDPE, LDPE, andmixtures thereof, in the amount of between 0.1 wt. % and 50 wt. %;wherein said first layer comprising HDPE is a core layer, said secondlayer comprising a metallocene polyethylene is a skin layer, and furthercomprising a second skin layer; wherein said first layer comprising HDPEis a core layer, said second layer comprising a metallocene polyethyleneis a skin layer, and further comprising a second skin layer, said secondskin layer comprising a metallocene polyethylene, which may be the sameor different from the first skin layer; wherein said first layercomprising HDPE is a core layer, said second layer comprising ametallocene polyethylene is a skin layer, and further comprising asecond skin layer, said second skin layer comprising an mLLDPE; whereinsaid first layer comprising HDPE is a core layer, said second layercomprising a metallocene polyethylene is a skin layer, and furthercomprising a second skin layer, said second skin layer comprising anmLLDPE and further comprising at least one additional polyolefinselected from group consisting of HDPE, LDPE, and mixtures thereof, inthe amount of between 0.1 wt. % and 50 wt. %; wherein said second skincomprises an mLLDPE and further comprises a polyolefin selected fromHDPE, LDPE, and mixtures thereof, in the amount of between 0.1 wt. % and50 wt. %; wherein none of the layers contain slip or antiblockadditives; any of the three or more layer structures wherein the totalthickness is 70 microns or less, 60 microns or less, 50 microns or less,preferably 40 microns or less, or even more preferably wherein saidfirst layer comprising HDPE has a thickness of about 40 microns or less,preferably 30 microns or less and each of said skin layers has athickness of about 10 microns or less, preferably 5 microns or less; andpreferably wherein the ratio of layers in the A/B/A structure describedherein is in the range of, respectively, (15±5):(70±10):(15±5), whereinthe structure is symmetrical or unsymmetrical with regard to one or moreof composition, dimensions, additional layers, and the like, e.g.,wherein the composition of the skin layers is identical or different,wherein there are additional layers, such as tie layers, between none,one or both of the A/B interfaces, wherein the ratio of layers A/B/A is15:70:15, 20/70/10, etc.

Another preferred embodiment is a film comprising an A/B/A structure,wherein the A layers are skin layers, which may be the same ordifferent, each independently are selected from a blend comprising anmPE having a density of between about 0.910 to 0.940 g/cm³, preferably0.915 to 0.940 g/cm³, and optionally an HDPE, which if present,preferably has a density of between about 0.940 and 0.970 g/cm³, morepreferably 0.955 to about 0.965 g/cm³, and most preferably from about0.960 to about 0.965 g/cm³, and/or optionally an LDPE, which if present,preferably has a density of from about 0.924 to about 0.940 g/cm³, orabout 0.916 to about 0.935 g/cm³, or about 0.926 to about 0.935 g/cm³,or about 0.916 to about 0.927 g/cm³, or about 0.921 to about 0.926g/cm³, or about 0.925 g/cm³ to about 0.930 g/cm³ 0.916 to 0.940 g/cm³,or about 0.924 to 0.935, and other embodiments including LDPEs havingdensities from any of the lower density limits specified to any of thehigher density limits specified herein, for example, 0.921 to 0.940g/cm³, 0.926 to 0.940 g/cm³, or 0.925 to 0.935 g/cm³ and the B is a corelayer comprising a blend comprising an HDPE, preferably having a densityof between about 0.940 and 0.970 g/cm³, more preferably 0.955 to about0.965 g/cm³, and most preferably from about 0.960 to about 0.965 g/cm³,and an LDPE, preferably having a density in the range of 0.916 to 0.935g/cm³, more preferably 0.925 to 0.930 g/cm³, and also including densityranges set forth previously for the one or more skin layer(s) and alsomore preferred embodiments of this A/B/A structure, wherein core layer Bcomprise 60-90 wt. %, more preferably 70-80 wt. % LDPE, and 40-10 wt. %HDPE, more preferably 30-20 wt. %, and skin layers A are eachindependently selected from 80-100 wt. %, preferably 85-95 wt. % mPE,and 20-0 wt. % HDPE, LDPE, or mixtures thereof, more preferably 15-5 wt.%; and a more preferred embodiment of any of the above embodimentswherein said layers A and layer B, when formed into a coextrudedstructure A/B/A having a total thickness of less than 60 microns or lessthan 50 microns, has a 1% secant Modulus MD of at least 335 mPa,preferably 400 mPa, more preferably 500 mPa, and a 1% secant Modulus TDof at least 335 mPa, preferably 400 mPa, more preferably 500 mPa, andstill more preferably 600 mPa, the secant Modulus values measure inaccordance with ASTM D882; and also any of the above embodiments whereinlayers A and layer B, when formed into a coextruded structure A/B/Ahaving a total thickness of less than 50 microns, has a difference inGloss 20° and 60° of 2% or less, the Gloss values measured in accordancewith ASTM D2457.

Additional preferred embodiments of any of the above would include thefilms having one or more of the performance parameters noted above inthe experimental section, and would also include films having additionallayers, such as A/B/C/D/E, wherein the skin layers A and E, which may bethe same or different, corresponding to the composition set forth abovefor skin layer A in the A/B/A structure or wherein A corresponds to theskin layer A and E corresponds to a layer comprising polypropylene, thecomposition C corresponds to the composition set forth above for corelayer B in the A/B/A structure, and B and D, which may be the same ordifferent, correspond to layers which may be selected from, withoutintending to be limiting, tie layers, reprocessed material layers and,in a preferred embodiment, additional layers having the compositioncorresponding to layer B in the A/B/A structure described previously.

In an embodiment, the structure comprising A/B/A layers as hereindescribe does not contain an oxygen barrier layer in the structure.However, one of the particularly beneficial uses of the collation shrinkcomprising the A/B/A layers according to the present invention is tooverwrap items having a primary oxygen barrier layer, e.g., perishableitems such as meats. Typical primary oxygen barriers are discussed in WO95/00333 recited above, such as vinylidene chloride copolymer, and mayalso include ethylene vinyl alcohol copolymers (EVOH copolymers).

Other preferred embodiments are coextruded films, heat shrinkable films,cast films, blown films, and collation shrink-wrapped structuresaccording to any of the preceding embodiments (including preferredembodiments, more preferred embodiments, etc.).

Trade names used herein are indicated by a ™ symbol or ® symbol,indicating that the names may be protected by certain trademark rights,e.g., they may be registered trademarks in various jurisdictions. Allpatents and patent applications, test procedures (such as ASTM methods,and the like), and other documents cited herein are fully incorporatedby reference to the extent such disclosure is not inconsistent with thisinvention and for all jurisdictions in which such incorporation ispermitted.

1. A film having two outer skin layers, each independently selected froma composition comprising: (a) 85-95 wt. % mLLDPE; and (b) 5-15 wt. % ofHDPE, LDPE, or a mixture thereof, a core layer comprising 60-90 wt. %LDPE and 40-10 wt. % HDPE, and wherein the film is no thicker than 50microns.
 2. A film having two outer skin layers, which may be the sameor different, each comprising: (a) an mPE prepared from ethylene and atleast one C₃ to C₁₂ alpha-olefin monomer and having a density of betweenabout 0.910 g/cm³ to about 0.940 g/cm³; and (b) HDPE, LDPE, or both,said HDPE having a density of between 0.940 and 0.970 g/cm³, and a corelayer comprising a blend comprising 60-90 wt. % LDPE and 40-10 wt. %HDPE, and wherein the film is no thicker than 50 microns.
 3. The filmaccording to claim 1, wherein said mLLDPE has a density of between 0.915to 0.940 g/cm³.
 4. The film according to claim 1, wherein the HDPE insaid core layer has a density of between 0.940 and 0.970 g/cm³.
 5. Thefilm according to claim 1, wherein said LDPE has a density of betweenabout 0.916 to 0.935 g/cm³.
 6. The film according to claim 1, whereinsaid two outer skin layers and said core layer, when formed into acoextruded structure having a total thickness of less than 50 microns,has a 1% secant Modulus MD of at least 400 mPa, and a 1% secant ModulusTD of at least 400 mPa, both measured in accordance with ASTM D882. 7.The film according to claim 6, wherein the 1% secant Modulus MD is atleast 500 mPa, and the 1% secant Modulus TD is at least 500 mPa,measured in accordance with ASTM D882.
 8. The film according to claim 1,wherein the core layer comprises 70-80 wt. % LDPE and 30-20 wt. % HDPE,and the skin layers are each independently selected from a blendcomprising 85-95 wt. % mLLDPE and 15-5 wt. % LDPE.
 9. The film accordingto claim 1, wherein each of said two outer skin layers and said corelayer have a total thickness of less than 50 microns, a difference inGloss 20° and 60° of 2% or less, where the Gloss values are measured inaccordance with ASTM D2457.
 10. The film according to claim 1, furthercomprising at least one layer between at least one of said outer skinand core layers, said at least one layer selected from the groupconsisting of a tie layer, a reprocessed material layer, and a layerselected from blends comprising an HDPE and an LDPE.
 11. A coextruded,heat-shrinkable film according to claim
 1. 12. A collationshrink-wrapped structure comprising a group of items wrapped by means ofa film according to claim
 1. 13. A process for making a packagedstructure, comprising wrapping a package with the film according toclaim 1, and heating the wrapped package to shrink the film and apply aholding force to the structure.
 14. The film according to claim 2,wherein at least one of said outer skin layers comprises HDPE and LDPE,said LDPE present in an amount of from 2 to 10 wt %, said HDPE having adensity of between 0.960 to 0.965 g/cm³.
 15. The film according to claim1, wherein said LDPE has a density of between 0.925 to 0.935 g/cm³. 16.The film according to claim 2, wherein said mPE is an mLLDPE having adensity of from about 0.918 to about 0.927 g/cm³.
 17. The film accordingto claim 16, wherein at least one of said outer skin layers furthercomprises an HDPE having a density of from about 0.940 to about 0.970g/cm³.
 18. The film according to claim 16, wherein the HDPE in said corelayer has a density of from about 0.940 to about 0.970 g/cm³.
 19. Thefilm according to claim 16, wherein said LDPE has a density of fromabout 0.916 to about 0.935 g/cm³.
 20. The film according to claim 16,wherein the core layer comprises 70-80 wt. % LDPE and 30-20 wt. % HDPE,and the skin layers are each independently selected from a blendcomprising 85-95 wt. % mPE and 15-5 wt. % LDPE.
 21. The film accordingto claim 16, wherein the outer skin layers and core layer, when formedinto a coextruded structure having a total thickness of less than 50microns, has a 1% secant Modulus MD of at least 400 MPa, and a 1% secantModulus TD of at least 400 MPa, both measured in accordance with ASTMD882.
 22. The film according to claim 21, wherein the coextrudedstructure has a 1% secant Modulus TD of at least 600 MPa, measured inaccordance with ASTM D882.
 23. The film according to claim 16, whereinsaid outer skin layers and core layer, when formed into a coextrudedstructure having a total thickness of less than 50 microns, has adifference in Gloss 20° and 60° of 2% or less, the Gloss values measuredin accordance with ASTM D2457.
 24. The film according to claim 16,further comprising at least one layer between at least one of said outerskin and core layers, said at least one layer selected from the groupconsisting of a tie layer, a reprocessed material layer, and a layerselected from blends comprising an HDPE and an LDPE.
 25. A coextruded,heat shrinkable film according to claim
 16. 26. A collationshrink-wrapped structure comprising a group of items wrapped by means ofa film according to claim
 16. 27. The film of claim 1, wherein themLLDPE is prepared from ethylene and at least one C₃ to C₁₂ alpha-olefinmonomer.
 28. The film of claim 1 or 2, wherein slip or antiblockadditives are excluded from the skin layer.
 29. The film of claim 1 or2, wherein slip or antiblock additives are excluded from the skin andcore layers.